An example of a multiplex communication device by a prior art spread spectrum communication system carrying out high speed data communication is indicated in FIGS. 6 and 7.
FIG. 6 represents a transmitter, in which reference numeral 1 is a serial-parallel convertor; 2-l.sub..about. 2-n are multipliers; 3-l.sub..about. 3-n are PN code generators; 4-l.sub..about. 4-n are BPSK modulators; and 5 is an adder.
In the transmitter inputted high speed data (A) are converted into parallel data sets (B1), (B2), . . . and (Bn) by the serial-parallel convertor 1. Each of the parallel data sets (B1), (B2), . . . and (Bn) is inputted to one of the inputs of each of the multipliers 2-1, 2-2, . . . and 2-n. On the other hand, each of PN codes (C1), (C2), . . . and (Cn) different from each other outputted by the PN code generators 3-1, 3-2, . . . and 3-n, respectively, is inputted to the other input of each of the multipliers 3-1, 3-2, . . . and 3-n. Outputs (D1), (D2), . . . and (Dn) of the multipliers 2-1, 2-2, . . . and 2-n are inputted to the BPSK modulators 4-1, 4-2, . . . and 4-n, respectively, to modulate a high frequency carrier signal (E). In this way high frequency signals (F1), (F2), . . . and (Fn) are outputted by the BPSK modulators 4-1, 4-2, . . . and 4-n, respectively, to be inputted to the adder 5. Finally a multiplexed speed spectrum signal (G) is outputted by the adder 5 to be transmitted.
FIG. 7 represents a receiver, in which 7-l.sub..about. 7-n are convolvers; 8-l.sub..about. 8-n are multipliers; 9-l.sub..about. 9-n are PN code generators; 10-l.sub..about. 10-n are detectors; and 12 is a data demodulator.
In the receiver described above a received signal (H) is distributed to be inputted to one of the inputs of each of the convolvers 7-1, 7-2, . . . and 7-n.
On the other hand, each of PN codes (K1), (K2), . . . and (Kn) outputted by the PN code generators 9-1, 9-2, . . . and 9-n is applied to one of the inputs of each of the multipliers 8-1, 8-2, . . . and 8-n, respectively. On the other hand, a high frequency carrier signal (L) is inputted to the other input of each of the multipliers 8-1, 8-2, . . . and 8-n. Each of outputs (I1), (I2), . . . and (In) of the multipliers 8-1, 8-2, . . . and 8-n is applied to the other input of each of the convolvers 7-1, 7-2, . . . 7-n, respectively.
Outputs (J1), (J2), . . . and (Jn) of the convolvers are inputted to the detectors 10-1, 10-2, . . . and 10-n, respectively. At this time a correlation spike is generated in each of the outputs of the convolvers with a same timing for every data channel. Outputs (M1), (M2), . . . and (Mn) of the detectors 10-1, 10-2, . . . and 10-n are inputted to the data demodulator 12. Reproduced data (N) are outputted by the data demodulator 12.
The prior art multiplex communication device described above has drawbacks that synchronization of the carrier signal is necessary and that it requires a plurality of convolvers (or matched filters) serving as correlators.